feat: rebrand to MMD PDF, single corporate theme, and remove original text under an edit

- Services/PdfRedactText.cs: strip text whose origin falls inside a CoverAnnotation
  from the page content stream at save time, hooked into PdfBurn.DrawAnnotationsIntoDoc.
  Fixes edited values staying recoverable by text extraction.
- Themes/MMD.xaml replaces all thirteen themes; picker and accent strip removed; no dark mode.
- Rename KillerPDF -> MMD PDF across code, resources, packaging and locale strings; new icon.
- Remove the upstream author credit and the in-app install button.

MmdPdf.Tests/WheelPageFlipGateTests.cs

@@ -0,0 +1,47 @@
+using MmdPdf.Services;
+using Xunit;
+
+namespace MmdPdf.Tests;
+
+public sealed class WheelPageFlipGateTests
+{
+    private static readonly DateTime Start = new(2026, 8, 22, 12, 0, 0, DateTimeKind.Utc);
+
+    [Fact]
+    public void TwoQuickNotchesAtEdge_ConfirmPageFlip()
+    {
+        var gate = new WheelPageFlipGate();
+
+        Assert.False(gate.TryConfirm(-120, Start));
+        Assert.True(gate.TryConfirm(-120, Start.AddMilliseconds(100)));
+    }
+
+    [Fact]
+    public void MomentumImmediatelyAfterContentScroll_DoesNotFlip()
+    {
+        var gate = new WheelPageFlipGate();
+        gate.NoteContentScroll(Start);
+
+        Assert.False(gate.TryConfirm(-120, Start.AddMilliseconds(50)));
+        Assert.False(gate.TryConfirm(-120, Start.AddMilliseconds(150)));
+    }
+
+    [Fact]
+    public void OppositeDirection_RestartsConfirmation()
+    {
+        var gate = new WheelPageFlipGate();
+
+        Assert.False(gate.TryConfirm(-120, Start));
+        Assert.False(gate.TryConfirm(120, Start.AddMilliseconds(100)));
+        Assert.True(gate.TryConfirm(120, Start.AddMilliseconds(200)));
+    }
+
+    [Fact]
+    public void SlowNotches_DoNotCombineIntoPageFlip()
+    {
+        var gate = new WheelPageFlipGate();
+
+        Assert.False(gate.TryConfirm(-120, Start));
+        Assert.False(gate.TryConfirm(-120, Start.AddMilliseconds(700)));
+    }
+}